1. Field of the Invention:
This invention relates to an apparatus for producing mineral wool type products from coal-ash, and particularly from the fly-ash component thereof.
2. Description of the Prior Art:
Mineral wool has become increasingly utilized for both thermal and accoustical insulation products. This is because mineral wool (or rock wool) fiber products compete favorably with other products in terms of durability, insulative quality, and cost.
Mineral wool is composed of interlaced fine mineral fibers which have the appearance of wool. Mineral wool is composed principally of silicates of calcium and alumina, along with other minor constituents, which are derived from common shale, clay, calcareous and siliceous materials, including metallurgical slags. Some of the foregoing materials require the addition of fluxes to produce suitable quality mineral wools. These fluxes include limestone, dolomite and fluorspar.
The conventional apparatus and method for making mineral wool is as follows. Lumps of raw material are mixed with coke (as fuel) inside a water jacketed, vertical cupola furnace. The coke is ignited and the heat produced is intensified by a supply of pre-heated combustion air fed into the cupola through a number of tuyeres situated in the lower portion of the furnace. As the coke burns, the raw material forms into a molten mass which flows in a continuous stream toward the bottom of the cupola. The stream of molten raw material then exits the cupola at a tap where it is subjected to spinning and blasting by high pressure air. The spinning/blasting step causes the molten raw material to solidify in long, fine strands. At the conclusion of the process, a mass of interlaced, wool-like mineral fibers has been produced.
Since the 1960's, research has been conducted concerning the production of mineral wool from coal-ash. Coal-ash is a by-product of coal fired furnaces and boilers. The coal-ash is produced by industry in very large quantities, posing a significant disposal problem. There are two components of coal-ash: "bottom-ash", often referred to as wet bottom boiler slag, and "fly-ash". Bottom-ash is generally dumped in disposal pits or reprocessed to serve as an additive for road construction materials. Fly-ash, on the other hand, is very powdery and therefore not safe for pit dumping because of wind-blown dust problems, is not a good additive for construction products (as the products tend to be weakened), and is not susceptible to being made into mineral wool products according to conventional systems.
Problematically, coal-ash is not suitable for melting in a cupola furnace for purposes of mineral wool manufacture because of its inherent powdery nature, which makes furnace operations susceptible to the danger of explosion. Further, coal-ash is not electrically conductive, and so is not susceptible for use in an electric arc furnace. There have been attempts in the prior art to directly transfer hot coal ash from the furnace in which it is being produced to a spinner stage so as to produce fibers. However, this process is impractical, as it is questionable whether the coal-ash is molten coming out of the furnace and, in any event, because of inevitable cool-down that will take place between the furnace location and the spinner stage location, resulting in fibers of dubious quality.
Other types of furnaces have proven unusable as well. In one known attempt by others to provide molten coal-ash for a spinner apparatus using an induction furnace, an explosion resulted due to the agitated molten metal eating into the water jacket of the furnace.
Accordingly, what is needed is an apparatus which will allow for the production of high quality mineral wool fibers from coal-ash.